Cellular transport occurs through the cell membrane and involves both passive and active transport mechanisms. The cell membrane is a lipid bilayer with embedded proteins that regulates what enters and exits the cell. Passive transport includes diffusion, facilitated diffusion, and osmosis, and does not require energy. Active transport uses energy to move molecules against their concentration gradient using carrier proteins. Bulk transport through endocytosis and exocytosis moves larger particles and molecules in and out of the cell. Osmosis, the diffusion of water through a semipermeable membrane, is important for cellular homeostasis and is affected by the solution's tonicity.

1. Cellular Transport
Notes

2. About Cell Membranes
1.All cells have a cell
membrane
2.Functions:
a.Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis
TEM picture of a
b.Provides protection and real cell membrane.
support for the cell

3. About Cell Membranes (continued)
3.Structure of cell membrane
Lipid Bilayer -2 layers of
phospholipids
a.Phosphate head is polar
(hydrophilic or water Phospholipid
loving)
b.Fatty acid tails non-polar
(hydrophobic or water
fearing)
c.Proteins embedded in Lipid Bilayer
membrane

4. Polar heads Fluid Mosaic
love water Model of the
& dissolve. cell membrane
Non-polar
Membrane move
tails hide
from water.
Carbohydrate cell
markers
Proteins

5. About Cell Membranes (continued)
• 4. Cell membranes have pores (holes) in it
a.Selectively permeable: Allows some
molecules in and keeps other molecules out
b.The structure helps it be selective!
Pores

6. About Cell Membranes (continued)
• 5. Size (macro or micro), charge (+ or -) and
solubility (lipid-soluble or not) affect a
molecule’s ability to cross the cell membrane.
 In general, small noncharged, lipid-soluble
molecules easily cross the cell membranes
Pores

7. Structure of the Cell Membrane
Outside of cell
Carbohydrate
Proteins chains
Lipid
Bilayer
Transport
Protein Phospholipids
Inside of cell
Animations
(cytoplasm)
of membrane
Go to structure
Section:

8. •Animations of Active
Types of Cellular Transport Transport & Passive
Transport
Weeee!!
• Passive Transport !
cell doesn’t use energy
1. Diffusion high
2. Facilitated Diffusion
3. Osmosis low
Tonicity
Water Potential This is
gonna
• Active Transport be hard
work!!
high
cell does use energy
low

9. Types of Cellular Transport
• Bulk Transport
1. Endocytosis
Phagocystosis
Pinocytosis
Receptor-mediated
2. Exocytosis

10. Passive Transport
• cell uses no energy
• molecules move randomly
• Molecules spread out from an area of
high concentration to an area of low
concentration.
• (HighLow)
• Three types:

11. 3 Types of Passive Transport
1. Diffusion
2. Facilitative Diffusion – diffusion with
the help of transport proteins ,
3. Osmosis – diffusion of water

12. Passive Transport:
Simple Diffusion A
1. Diffusion
1. Diffusion: random movement
of particles from an area of
high concentration to an
area of low concentration.
(High to Low)
• Diffusion continues until all
molecules are evenly spaced
(equilibrium is reached)-Note:
molecules will still move around
but stay spread out.
http://bio.winona.edu/berg/Free.htm

13. Passive Transport:
1. Diffusion
• Occurs in liquid or gas medium
Diffusion of a solute within a solvent is
affected by several factors:
 Temperature
 Pressure
 Density of the solvent
 Concentration Gradient
 Solubility of the solute
http://bio.winona.edu/berg/Free.htm

14. Passive Transport:
2. Facilitated Diffusion
2. Facilitated diffusion: diffusion of specific particles
through membrane transport proteins to help them move
through the cell membrane
a. Transport Proteins are specific – they “select” only
certain molecules to cross the membrane
b. Transports larger or charged molecules
c. Concentration gradient required – can’t transport from
low to high concentration
d. Energy not needed
e. Rate of transport reaches a maximum when all
membrane transport proteins are used up (saturated)
f. Membrane transport proteins are sensitive to inhibitors
that can cause them not to function

15. Passive Transport:
2. Facilitated Diffusion A B
There are 2 types of
membrane transport
proteins involved:
Channel proteins – contain
tunnels/openings that serve
as passageways of Facilitated
molecules Diffusion
diffusion (Lipid
Carrier proteins – undergo (Channel Bilayer)
temporary binding to the Protein)
molecule it carries resulting
in conformational change
that moves the molecule
through the membrane
Carrier Protein

16. Passive Transport: 2. Facilitated Diffusion
Glucose
molecules
Cellular Transport From a-
High
High Concentration
• Channel Proteins
animations
Cell Membrane
Protein
Low Concentration
Low
channel
Transport
Through a 
Go to
Protein
Section:

17. Passive Transport: Osmosis
3. Osmosis animation
• 3.Osmosis: diffusion of
water through a
selectively permeable
membrane
•Water moves freely
through pores.
•Solute (green) to large
to move across.

18. The water molecules will continue to cross the semi-permeable
membrane until an equilibrium is reached, where the two solutions
are of equal concentration.

19. Passive Transport:
3. Osmosis
Water is found inside and outside of the cell,
separated by a semi-permeable membrane
The presence of different solutes in the water
solutions in and out of the cell means concentration
of water on both sides is different.
Water Potential – term for movement of water
molecules as it undergoes osmosis
- The measure of the difference between the “force”
that pushes water molecules and the “force” exerted
by the membrane

20. Passive Transport:
3. Osmosis
Water solution with less solute (more diluted solution because of more water) =
higher water potential
Water solution with more solute (more concentrated solution) = lower water
potential
Water Potential Gradient - when 2 solutions of different water potentials are
separated by a semipermeable membrane, thus allowing osmosis to occur
Osmotic Pressure – “force” that moves water molecules through a semi-
permeable membrane

21. Passive Transport:
3. Osmosis
Tonicity – strength
of a solution in
relation to osmosis
3 Types:
Isotonic
Hypotonic
Hypertonic
Remember: Salt is a solute, when it is concentrated inside or outside
the cell, it will draw the water in its direction. This is also why you
get thirsty after eating something salty.

22. If the concentration of solute (salt) is equal on both sides, the water will
move back in forth but it won't have any result on the overall amount of
water on either side.
"ISO" means the same

23. "HYPO" means less
In this case there are less solute
(salt) molecules outside the cell,
since salt sucks, water will move
into the cell, causing it to swell.
The cell will gain water and grow
larger. As osmosis continues,
osmotic pressure builds up inside
the cell causing cell lysis.
In plant cells, the vacuoles will fill and the plant becomes stiff and rigid.
The pressure exerted by the water molecule is called TURGOR
PRESSURE, and the phenomenon TURGIDITY. The turgor pressure in
plants will not result in cell lysis as the cell wall keeps the plant from
bursting.
TURGIDITY is important in maintaining the firm and erect position of a
plant.

24. "HYPER" means more
In this case there are more solute (salt) molecules outside the cell, which
causes the water to be sucked in that direction.
Causes cells to shrink and lose shape because of water loss.
In plant cells, the central vacuole loses water and the cells shrink, causing
wilting (plasmolysis). In animal cells, the cells also shrink.
In both cases, the cell may die.

26. Active Transport
•cell uses energy (ATP or Adenosine Triphosphate)
•actively moves molecules to where they are needed
•Movement of molecules against concentration gradient
(concentration gradient not required)
•Movement from an area of low concentration to an
area of high concentration (Low  High)
•Transport proteins are highly specific
•Involves carrier proteins (like facilitated diffusion) often
called pumps because they use energy to move
molecules against a concentration gradient

27. Sodium
Example: Sodium Potassium Pumps
-Potassium Pumps (Active Transport
using proteins)
are important in nerve
responses. They
transfer Na and K
ions in and out of the
nerve and muscle
cells.
Protein changes
shape to move
molecules: this
requires energy!

28. Types of Bulk Transport
1. Endocytosis: taking bulky
material that can’t use transport
proteins (like macromolecules)
into a cell
• Uses energy
• Cell membrane in-folds
around the macromolecule to
be transported
• 3 Types:
 Phagocytosis
 Pinocytosis
 Receptor-mediated
Endocytosis

29. Types of Bulk Transport
Phagocytosis – “cell eating”
- Process by which cells take in large particles by
infolding the cell membrane to form endocytotic
vesicles
Ex. WBC capture and kill invading bacteria

30. Types of Bulk Transport
Pinocytosis – “cell drinking”
- Process of taking in fluids into the cell by invagination
of the cell membrane. Any solute or small particles
in the fluid will be moved into the cell.

31. Types of Bulk Transport
Receptor-mediated Endocytosis – “cell drinking”
- Compared to pinocytosis, is very specific. The plasma membrane
becomes indented and forms a pit. The pit lined with receptor proteins
picks specific molecules from its surroundings. The pit will close and pinch
off to form a vesicle which will carry the molecules inside the cytoplasm.

32. Types of Active Transport
2. Exocytosis: Forces Endocytosis &
Exocytosis
material out of cell in animations
bulk
• membrane surrounding the
material fuses with cell
membrane
• Cell changes shape –
requires energy
• EX: Hormones or
wastes released from
cell

33. Effects of Osmosis on Life
• Osmosis- diffusion of water through a
selectively permeable membrane
• Water is so small and there is so much
of it the cell can’t control it’s movement
through the cell membrane.

34. • Osmosis
Animations for
Hypotonic Solution isotonic, hypertonic,
and hypotonic
solutions
Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than
inside the cell. (Low solute; High water)
Result: Water moves from the solution to inside the
cell): Cell Swells and bursts open (cytolysis)!

35. • Osmosis
Animations for
Hypertonic Solution isotonic, hypertonic,
and hypotonic
solutions
Hypertonic: The solution has a higher concentration
of solutes and a lower concentration of water than
inside the cell. (High solute; Low water)
shrinks
Result: Water moves from inside the cell into the
solution: Cell shrinks (Plasmolysis)!

36. • Osmosis
Animations for
Isotonic Solution isotonic, hypertonic,
and hypotonic
solutions
Isotonic: The concentration of solutes in the solution
is equal to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and
the cell remains same size! (Dynamic Equilibrium)

37. What type of solution are these cells in ?
A B C
Hypertonic Isotonic Hypotonic

38. How Organisms Deal • Paramecium
(protist) removing
excess water
with Osmotic Pressure video
•Bacteria and plants have cell walls that prevent them
from over-expanding. In plants the pressure exerted on
the cell wall is called tugor pressure.
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.

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